34 T. STERRY HUNT ON THE GENETIC 
publications of the Geological Survey of Canada, in 1863, and farther in 1866. À summary 
of these results will be found in the writers volume on Azoic Rocks, page 154. 
$ 62. As regards the genesis, according to the crenitic hypothesis, of the various 
mineral species found in this vast crystalline series, alike in the more ancient strata and 
in their included endogenous masses, we have already considered the formation of the 
double silicates of alumina with alkalies and lime, represented by the various feldspars, 
and more rarely by the scapolites, epidote, garnet, and the muscovitic or non-magnesian 
micas. These latter, though abundant, with garnet and black tourmaline, in some 
granitic veins in this geological series, are rare in those portions in which the pro- 
toxyd-silicates abound; while the silicates of alumina without protoxyd-bases, such 
as are andalusite, fibrolite, cyanite, topaz, and pyrophyllite, are unknown. On the other 
hand, aluminous double silicates with magnesia are abundantly represented by phlo- 
gopite, and protoxyd-silicates with magnesia, such as chondrodite, pyroxene, and amphi- 
bole, are abundant ; the simple calcareous silicate, wollastonite, being more rarely met 
with. The genesis of all these we have supposed to be by the reaction of soluble cal- 
careous silicates with magnesian and ferrous solutions. The magnesia required may be 
found either in salts like those of sea-water, or in solutions of magnesian bicarbonate from 
subaerial decay of plutonic rocks, which solutions, by reacticn with lime-silicates, would 
give rise to insoluble magnesian compounds and soluble lime-carbonate. A similar reac- 
tion, with liberation of silica, would result from the direct operation of carbonic-dioxyd 
upon the lime-silicate. The intervention of ferrous solutions in similar reactions has 
already been discussed in considering the origin of glauconite, in § 10-12. 
§ 63. As regards the presence in these, and similar crystalline rocks, of basic oxyds 
uncombined with silica or with carbonic acid, such as alumina and magnesia in corun- 
dum; spinel and some chromites ; chromic oxyd in the latter and in some spinels; glucina 
and magnesia in chrysoberyl and periclase ; together with zinc, manganese and iron-oxyds 
in spartalite, franklinite, magnetite, and hematite; not to mention titanic oxyd in rutile, 
and in menaccanite and other titanates,—it should be noticed that these various compounds 
for the most part occur in such intimate association with certain silicates as to suggest 
their contemporaneous production. Thus corundum and spinel are found crystallized 
with certain micas, with chlorites, or with feldspars, pyroxene or chrysolite, in which 
latter, or in serpentine, chromite is generally met with. Spartalite and franklinite are 
associated with silicates of zinc and manganese, and magnetite with quartz, with ortho- 
clase, with pyroxene, with chondrodite, or with chrysolite ; while rutile and menaccanite 
are found in like manner with feldspars, with phlogopite, or with serpentine. The inti- 
mate association of magnetite with calcite, with apatite, with pyrite, and with graphite, 
in these deposits, may also be noticed. We must conclude that all these simple and com- 
pound oxyds have been in solution, and have crystallized in the presence of the various 
silicates, etc., and in many cases with quartz. It is evident that the partial reduction 
and solution of ferrous oxyd by the intervention of the products of organic decay, and its 
subsequent precipitation, which in later times, has played so large a part in the genesis 
of iron-oxyds and carbonate, is not the sole agency. A process which separates not only 
iron-oxyd, but chrome-oxyd, alumina, glucina, magnesia, and zinc and manganese-oxyds 
from their silicated combinations, and has permitted them to crystallize side by side with 
silicates, and even with free silica, has intervened in the genesis of these ancient crenitic 
